Certain applications require that fluid flowing through a conduit is heated prior to the fluid flowing into a component at a downstream end of the conduit. For example, a space launch vehicle with a liquid propellant rocket engine requires that cryogenic oxidizer (e.g., liquid oxygen—LOX) and cryogenic fuel (e.g., liquid hydrogen—LH2) are heated just prior to entering the engine section to ensure quality of ignition and combustion during an engine start. Heating cryogenic propellants is complicated by the fact that the cryogenic propellant tanks are located above the engine. For example, LOX may flow downwardly through a relatively large diameter conduit from a LOX tank located a significant distance (e.g., up to 100 feet or more) above the engine.
Due to the relatively large diameter of the conduit and the initially low flow requirements for engine start, the LOX is initially relatively slow moving through the conduit. During heating of the LOX by heaters located outside the conduit, the LOX immediately adjacent the inner surface of the conduit wall is converted into a relatively low density buoyant flow that moves upwardly along the conduit inner surface, while a remainder of the higher density heated LOX flows downwardly into the engine. Due to the relatively large diameter of the conduit and the relatively low flow rate of the LOX, the upwardly-moving buoyant flow draws a portion of the heated LOX upwardly through the conduit.
The net effect of the upward flow of heated LOX is a loss in the efficiency of the heaters, requiring an increase in the power output of the heaters and/or an increase in the quantity of heaters as a means to heat the LOX to the required temperature for engine start. Unfortunately, increasing the power level of the heaters reduces the operating efficiency of the engine start system. Increasing the quantity of heaters increases the cost and weight of the launch vehicle. In addition, the power density of the heaters can reach a maximum point where no additional heat can be added to the LOX. Furthermore, a portion of heated LOX moving upwardly through the conduit may flow into the LOX tank and heat the bulk liquid in the tank, resulting in a reduction in the density of the bulk liquid and a corresponding reduction in the amount of available propellant mass. The reduction in propellant mass reduces the amount of payload that can be launched into space.
As can be seen, there exists a need in the art for a system and method for increasing the efficiency of heating cryogenic fluid flowing in a conduit.